1. Field of the Invention
The present invention relates to a flame-retardant thermoplastic resin composition containing a surface-treated inorganic filler by which humidity- and heat-resistance are improved.
2. Description of the Background
Flame-retardancy has been conventionally imparted using various aromatic orthophosphates as a flame-retardant in a thermoplastic resin. It is also well known that a variety of inorganic fillers can be added as a reinforcing agent and an extender of the resin composition, as required.
However, when an aromatic orthophosphate is used as a flame-retardant and inorganic fillers are used as a reinforcing agent and an extender in a thermoplastic resin, the properties of these additives are generally satisfactory immediately after their addition, except that humidity resistance and heat resistance are greatly decreased.
In order to solve these problems, for example, an aromatic orthophosphate having a good humidity resistance and a good heat resistance may be selected, and humidity resistance and heat resistance can be improved by surface-treating an inorganic filler using various surface treating agents, as reported in Japanese Patent Publication No. 18,336/1990 and a Japanese Patent Application Laid-Open (Kokai) No. 36,630/1989.
As the above-mentioned surface treating agent of the inorganic filler, an aliphatic acid compound, a silane compound, a titanate compound and a phosphorus compound are known. However, the aliphatic acid compound exhibits a low surface treatment effect to the inorganic filler. In order to retain a high surface treatment effect, a large amount of the surface treating agent is required, with the result that the properties of the blend are disadvantageously compromised. Moreover, the silane compound which is a surface treating agent has, itself, poor hydrolysis resistance. Therefore, the properties are notably decreased when conducting the test for humidity resistance. Further, the titanate compound, is, itself, discolored. Accordingly, a composition containing an inorganic filler treated with this compound is discolored.
With respect to the phosphorus compound, it is reported in Japanese Patent Application Laid-Open (Kokai) No. 36,630/1989, that humidity resistance can be improved using a dialkyl phosphate or a monoalkyl phosphate. In this case, however, humidity resistance and heat resistance of a thermoplastic resin composition containing an inorganic filler obtained through surface-treatment with the phosphorus compound could not be satisfied. Further, an unsaturated alkyl phosphoric acid diester or monoester is reported in Japanese Patent Publication No. 58,173/1988. Nevertheless, observed flame-retardancy is inadequate, and when an organic filler is used in a large amount to impart flame-retardancy, properties of a blend are decreased.